Power supply system

ABSTRACT

A power supply system includes a plurality of sweep modules that is connected to a main line. Each sweep module includes a switching element that switches between connection and disconnection between a battery module and the main line and is formed of a MOSFET. A failure detecting device of the power supply system includes a temperature detecting unit configured to detect temperatures of the plurality of sweep modules and a failure determining unit configured to determine whether a difference between a temperature of one sweep module selected from the plurality of sweep modules and a reference temperature which is determined based on the temperatures of other sweep modules is greater than a predetermined threshold value.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2018-223364 filed onNov. 29, 2018 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The disclosure relates to a power supply system that includes aplurality of modules of which each includes a battery and a circuit.

2. Description of Related Art

A power supply system that includes a plurality of modules of which eachincludes a battery and a circuit and performs at least one of outputtingof electric power to the outside and storage of electric power which isinput from the outside by controlling the plurality of modules is known.For example, a power supply device (a power supply system) described inJapanese Patent Application Publication No. 2018-74709 (JP 2018-74709 A)includes a plurality of battery circuit modules of which each includes abattery, a first switching element, and a second switching element. Theplurality of battery circuit modules is connected in series with outputterminals interposed therebetween. A control circuit of the power supplydevice outputs a gate signal for switching the first switching elementand the second switching element between ON and OFF to the batterycircuit modules at intervals of a predetermined time. Accordingly, atarget electric power is output from the plurality of battery circuitmodules.

SUMMARY

In the power supply device described in JP 2018-74709 A, a metal oxidesemiconductor field effect transistor (MOSFET) is used as the switchingelements which are provided in each battery circuit module. Since aMOSFET structurally includes a body diode (a parasitic diode), a currentmay flow in a circuit in the power supply device via the body diode evenwhen a disconnection failure has occurred in a driving circuit of aswitching element or the like. In this case, although the switchingelement has a disconnection failure, electric power can be input to andoutput from the power supply device as a whole and thus there is concernthat the failure will be detected late. On the other hand, there isdemand for early detection of a position at which a switching elementhas a failure.

According to an aspect of the disclosure, there is provided a powersupply system including a main line, a plurality of sweep modules thatis connected to the main line, and a failure detecting device. Eachsweep module includes a battery module, an input and output circuit thatis configured to connect the battery module to the main line, at leastone switching element that is provided in the input and output circuit,is configured to switch between connection and disconnection between thebattery module and the main line, and is formed of a MOSFET, and aswitching control unit configured to transmit a gate signal to the atleast one switching element. The failure detecting device of the powersupply system includes a temperature detecting unit configured to detecttemperatures of the plurality of sweep modules and a failure determiningunit configured to determine whether a difference (T_(m)−T_(s)) betweena temperature T_(m) of one sweep module selected from the plurality ofsweep modules and a reference temperature T_(s) which is determinedbased on the temperatures of other sweep modules is greater than apredetermined threshold value ΔT_(th).

With attention on the fact that a switching element formed of a MOSFETemits heat to increase the temperature of the sweep module when acurrent flows via a body diode of the switching element, the inventorinvented the power supply system having the above-mentionedconfiguration. That is, the failure determining unit of the power supplysystem determines whether a difference (T_(m)−T_(s)) between atemperature T_(m) of one sweep module (a sweep module which is aninspection object) selected from the plurality of sweep modules and areference temperature T_(s) which is determined based on thetemperatures of the other sweep modules is greater than a predeterminedthreshold value ΔT_(th). In this way, by comparing the temperature T_(m)of the sweep module which is an inspection object with the referencetemperature T_(s) based on the other sweep modules and determiningwhether an excessive increase in temperature greater than the thresholdvalue ΔT_(th) occurs, it is possible to easily detect whether aswitching element of a sweep module which is an inspection object has afailure.

In the power supply system according to the aspect, the failuredetermining unit may be configured to sequentially determine whether thedifference (T_(m)−T_(s)) is greater than the predetermined thresholdvalue ≢6T_(th) while changing the sweep module which is selected fromthe plurality of sweep modules. In this way, by sequentially performingthe above-mentioned failure determining process on the plurality ofsweep modules, it is possible to easily identify a sweep module in whicha switching element has a failure.

In the power supply system according to the aspect, the referencetemperature T_(s) may be an average value T_(ave-m) of the temperaturesof the other sweep modules other than the sweep module which is selectedfrom the plurality of sweep modules. By using the average valueT_(ave-m) of the temperatures of the other sweep modules other than thesweep module which is an inspection object as the reference temperatureT_(s) in the failure determining process, it is possible to accuratelydetermine whether a switching element has a failure even when a slightmeasurement error occurs due to a surrounding environment of thetemperature detecting unit or operating conditions of the power supplysystem.

In the power supply system according to the aspect, each sweep modulemay include: a first switching element that is attached in series to themain line and in parallel to the battery module; and a second switchingelement that is attached to the input and output circuit such that thebattery module is connected in series to the main line. The switchingcontrol unit may be configured to transmit a connection signal forconnecting the battery module to the main line by turning off the firstswitching element and turning on the second switching element and adisconnection signal for disconnecting the battery module from the mainline by turning on the first switching element and turning off thesecond switching element. The temperature detecting unit may include: atemperature sensor that is disposed at an intermediate position betweenthe first switching element and the second switching element; and aprocessing unit configured to detect the temperature of the sweep modulebased on a signal transmitted from the temperature sensor. As in thisaspect, when the first switching element and the second switchingelement are provided and a temperature sensor is disposed at anintermediate position between the switching elements, emission of heatdue to a disconnection failure of a switching element can be accuratelydetected using one temperature sensor, which is desirable in view of adecrease in the number of components.

In the aspect in which two switching elements are provided, the failuredetermining unit may be configured to select a sweep module to which theconnection signal has been transmitted from the switching control unitwhen a charging current is flowing in the main line and to determinethat the second switching element of the selected sweep module has afailure when the difference (T_(m)−T_(s)) between the temperature T_(m)of the selected sweep module and the reference temperature T_(s) isgreater than the predetermined threshold value ΔT_(th). In the aspect inwhich the first switching element and the second switching element areprovided, when the second switching element has a failure in a state inwhich the connection signal is transmitted from the switching controlunit and a charging current flows in the main line, a current flows inthe second switching element via the body diode and the second switchingelement emits heat. According to this aspect, it is possible to easilydetect whether the second switching element of a sweep module which isan inspection object has a failure by determining whether the secondswitching element emits heat.

In the aspect in which two switching elements are provided, the failuredetermining unit may be configured to select a sweep module to which thedisconnection signal has been transmitted from the switching controlunit when a discharging current is flowing in the main line and todetermine that the first switching element of the selected sweep modulehas a failure when the difference (T_(m)−T_(s)) between the temperatureT_(m) of the selected sweep module and the reference temperature T_(s)is greater than the predetermined threshold value ΔT_(th). In the aspectin which the first switching element and the second switching elementare provided, when the first switching element has a failure in a statein which the disconnection signal is transmitted from the switchingcontrol unit and a discharging current flows in the main line, a currentflows in the first switching element via the body diode and the firstswitching element emits heat. According to this aspect, it is possibleto easily detect whether the first switching element of a sweep modulewhich is an inspection object has a failure by determining whether thefirst switching element emits heat.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a diagram schematically illustrating a configuration of apower supply system 1;

FIG. 2 is a diagram schematically illustrating a configuration of asweep module 20;

FIG. 3 is a timing chart illustrating an example of a sweep operation;

FIG. 4 is a timing chart illustrating an example of a forcible throughoperation;

FIG. 5 is a schematic configuration diagram illustrating determinationof a failure of a second switching element; and

FIG. 6 is a schematic configuration diagram illustrating determinationof a failure of a first switching element.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an exemplary embodiment of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Detailswhich are not particularly mentioned in this specification and which arerequired for embodiment can be understood as design details based on therelated art by those skilled in the art. The disclosure can be embodiedbased on details described in this specification and common generaltechnical knowledge in the art. In the following drawings, members andparts performing the same operations will be referred to by the samereference signs. The dimensional relationships in the drawings do notreflect actual dimensional relationships.

<Overall Schematic Configuration>

The overall configuration of a power supply system 1 according to anembodiment will be schematically described below with reference toFIG. 1. The power supply system 1 performs at least one of outputting ofelectric power to a power distribution device 5 which is connected to ahost power system 8 and storage of electric power which is input fromthe power distribution device 5 (hereinafter simply referred to as“inputting and outputting of electric power”). For example, in thisembodiment, a power conditioning subsystem (PCS) is used as the powerdistribution device 5. The PCS has a function of converting electricpower input from the power system 8 to the power supply system 1 or thelike and electric power output from the power supply system 1 or thelike to the power system 8 between the power supply system 1 or the likeand the power system 8.

When electric power is surplus to the power system 8, the powerdistribution device 5 outputs the surplus electric power to the powersupply system 1. In this case, the power supply system 1 stores electricpower which is input from the power distribution device 5. The powersupply system 1 outputs electric power stored in the power supply system1 to the power distribution device 5 in accordance with an instructionfrom a host system 6 that controls the host power system 8. In FIG. 1,the host system 6 is a system that controls the power system 8 and thepower distribution device 5 and is provided separately from the powersystem 8 and the power distribution device 5. However, the host system 6may be incorporated into the power system 8 or the power distributiondevice 5.

The power supply system 1 includes one or more strings 10. The powersupply system 1 according to this embodiment includes a plurality of (N:N≥2) strings 10 (10A, 10B, . . . , 10N). In FIG. 1, for the purpose ofconvenience, only two strings 10A and 10B out of the N strings 10 areillustrated. Each string 10 serves as a unit for inputting andoutputting electric power to and from the power distribution device 5.The plurality of strings 10 is connected in parallel to the powerdistribution device 5. Inputting and outputting (power supply) ofelectric power between the power distribution device 5 and each string10 is performed via a main line 7.

Each string 10 includes a string control unit (SCU) 11 and a pluralityof (M: M≥2) sweep modules 20 (20A, 20B, . . . , 20M). Each sweep module20 includes a battery and a control circuit. The SCU 11 is provided foreach string 10. The SCU 11 is a controller that comprehensively controlsthe plurality of sweep modules 20 included in the corresponding string10. Each SCU 11 communicates with a group control unit (GCU) 2 servingas a power control device. The GCU 2 is a controller thatcomprehensively controls a group including the plurality of strings 10as a whole. The GCU 2 communicates with the host system 6 and the SCUs11. Various methods (for example, at least one of wired communication,wireless communication, and communication via a network) can be employedas a method of communication between the host system 6, the GCU 2, andthe SCUs 11.

The configuration of the controllers that control the strings 10, thesweep modules 20, and the like may be modified. For example, the GCU 2and the SCUs 11 may not be separately provided. That is, one controllermay control the whole group including one or more strings 10 and all theplurality of sweep modules 20 included in the string 10.

<Sweep Module>

A sweep module 20 will be described below in detail with reference toFIG. 2. The sweep module 20 includes a battery module 30, a powercircuit module 40, and a sweep unit (SU) 50.

The battery module 30 includes at least one battery 31. A plurality ofbatteries 31 is provided in the battery module 30 according to thisembodiment. The plurality of batteries 31 is connected in series. Inthis embodiment, a secondary battery is used as each battery 31. Atleast one of various secondary batteries (for example, a nickel-hydridebattery, a lithium ion battery, and a nickel-cadmium battery) can beused as the battery 31. In the power supply system 1, a plurality oftypes of batteries 31 may be mixed. The types of the batteries 31 in allthe battery modules 30 may be the same.

A voltage detecting unit 35 and a temperature detecting unit 36 areprovided in the battery module 30. The voltage detecting unit 35 detectsa voltage of the batteries 31 in the battery module 30 (the plurality ofbatteries 31 connected in series in this embodiment). The temperaturedetecting unit 36 detects a temperature of the batteries 31 in thebattery module 30 or a temperature near the batteries 31. Variousdevices (for example, a thermistor) that detect a temperature can beused as the temperature detecting unit 36.

The battery module 30 is provided to be attached to and detached fromthe power circuit module 40. Specifically, in this embodiment, with thebattery module 30 including a plurality of batteries 31 as one unit,detachment of the battery module 30 from the power circuit module 40 andattachment thereof to the power circuit module 40 are performed.Accordingly, in comparison with a case in which the batteries 31 in thebattery module 30 are replaced one by one, the number of operation stepswhen an operator replaces the batteries 31 decreases. In thisembodiment, the voltage detecting unit 35 and the temperature detectingunit 36 are replaced separately from the battery module 30. However, atleast one of the voltage detecting unit 35 and the temperature detectingunit 36 may be replaced along with the battery module 30.

The power circuit module 40 forms a circuit for appropriately realizinginputting and outputting of electric power in the battery module 30. Inthis embodiment, the power circuit module 40 includes at least oneswitching element that switches between connection and disconnectionbetween the battery module 30 and the main line 7. In this embodiment,the power circuit module 40 includes an input and output circuit 43 thatconnects the battery module 30 to the main line 7 and a first switchingelement 41 and a second switching element 42 that are provided in theinput and output circuit 43. The first switching element 41 and thesecond switching element 42 perform a switching operation in accordancewith a signal (for example, a gate signal) which is input from the sweepunit 50.

In this embodiment, as illustrated in FIG. 2, the first switchingelement 41 is attached in series to the main line 7 and in parallel tothe battery module 30 in the input and output circuit 43. The secondswitching element 42 is attached to a part of the input and outputcircuit 43 that connects the battery module 30 in series to the mainline 7. A source and a drain of the first switching element 41 aredisposed such that a forward direction thereof is set to a direction inwhich a discharging current flows in the main line 7. A source and adrain of the second switching element 42 are disposed in the input andoutput circuit 43 attaching the battery module 30 in series to the mainline 7 such that a forward direction thereof is set to a direction inwhich a charging current flows in the battery module 30. In thisembodiment, the first switching element 41 and the second switchingelement 42 are MOSFETs (for example, Si-MOSFETs) and include body diodes41 a and 42 a, respectively, set to a forward direction. Here, the bodydiode 41 a of the first switching element 41 can be appropriatelyreferred to as a first body diode. The body diode 42 a of the secondswitching element 42 can be appropriately referred to as a second bodydiode.

The first switching element 41 and the second switching element 42 arenot limited to the example illustrated in FIG. 2. Various elements thatcan switch between connection and disconnection can be used as the firstswitching element 41 and the second switching element 42. In thisembodiment, a MOSFET (specifically an Si-MOSFET) is used as both thefirst switching element 41 and the second switching element 42. However,an element (for example, a transistor) other than a MOSFET may beemployed.

The power circuit module 40 includes an inductor 46 and a capacitor 47.The inductor 46 is provided between the battery module 30 and the secondswitching element 42. The capacitor 47 is connected in parallel to thebattery module 30. In this embodiment, since secondary batteries areused as the batteries 31 of the battery module 30, it is necessary tocurb deterioration of the batteries 31 due to an increase in internalresistance loss. Accordingly, by forming an RLC filter using the batterymodule 30, the inductor 46, and the capacitor 47, equalization of acurrent is achieved.

A temperature detecting unit 48 is provided in the power circuit module40. The temperature detecting unit 48 is provided to detect emission ofheat from at least one of the first switching element 41 and the secondswitching element 42. In this embodiment, the first switching element41, the second switching element 42, and the temperature detecting unit48 are assembled into one base. Accordingly, the base is replaced at atime point at which a defect of one of the first switching element 41and the second switching element 42 has been detected. Accordingly, inthis embodiment, by providing one temperature detecting unit 48 near thefirst switching element 41 and the second switching element 42, it ispossible to decrease the number of components. Here, a temperaturedetecting unit that detects the temperature of the first switchingelement 41 and a temperature detecting unit that detects the temperatureof the second switching element 42 may be provided separately from eachother. Various devices (for example, a thermistor) that detect atemperature can be used as the temperature detecting unit 48.

As illustrated in FIGS. 1 and 2, a plurality of battery modules 30 inthe string 10 are connected in series to the main line 7 with thecorresponding power circuit modules 40 interposed therebetween. Byappropriately controlling the first switching element 41 and the secondswitching element 42 of each power circuit module 40, the correspondingbattery module 30 is connected to the main line 7 or is disconnectedfrom the main line 7. In the example of the configuration of the powercircuit module 40 illustrated in FIG. 2, when the first switchingelement 41 is turned off and the second switching element 42 is turnedon, the battery module 30 is connected to the main line 7. When thefirst switching element 41 is turned on and the second switching element42 is turned off, the battery module 30 is disconnected from the mainline 7.

The sweep unit (SU) 50 is a control unit that is incorporated into thesweep module 20 such that various controls associated with the sweepmodule 20 are executed, and is also referred to as a sweep control unit.Specifically, the sweep unit 50 outputs a signal for driving the firstswitching element 41 and the second switching element 42 in the powercircuit module 40. The sweep unit 50 notifies a host controller (the SCU11 illustrated in FIG. 1 in this embodiment) of states of the sweepmodule 20 (for example, the voltage of the battery module 30, thetemperature of the batteries 31, and the temperature of the switchingelements 41 and 42). The sweep unit 50 is incorporated into each of aplurality of sweep modules 20 of each string 10. The sweep units 50incorporated into the plurality of sweep modules 20 of each string 10are sequentially connected to each other and are configured to allow agate signal GS which is output from the SCU 11 to propagatesequentially. As illustrated in FIG. 2, in this embodiment, each sweepunit 50 includes an SU processing unit 51, a delay/selection circuit 52,and a gate driver 53.

The SU processing unit 51 is a controller that takes charge of variousprocesses in the sweep unit 50. For example, a microcomputer can be usedas the SU processing unit 51. Detection signals from the voltagedetecting unit 35, the temperature detecting unit 36, and thetemperature detecting unit 48 are input to the SU processing unit 51.The SU processing unit 51 performs inputting and outputting varioussignals to and from a host controller (the SCU 11 of the string 10 inthis embodiment).

The signals which are input from the SCU 11 to the SU processing unit 51include a forcible through signal CSS and a forcible connection signalCCS. The forcible through signal CSS is a signal for instructing todisconnect the battery module 30 from the main line 7 (see FIG. 1)extending from the power distribution device 5 to the string 10. Thatis, the sweep module 20 to which the forcible through signal CSS isinput ignores an operation for inputting and outputting electric powerto and from the power distribution device 5. The forcible connectionsignal CCS is a signal for instructing to maintain connection of thebattery module 30 to the main line 7.

A gate signal GS is input to the delay/selection circuit 52. The gatesignal (a PWM signal in this embodiment) GS is a signal for controllingan alternate repeated switching operation between an ON state and an OFFstate of the first switching element 41 and the second switching element42. The gate signal GS is a pulse-shaped signal in which ON and OFF arealternately repeated. The gate signal GS is first input to thedelay/selection circuit 52 in one sweep module 20 from the SCU 11 (seeFIG. 1). Subsequently, the gate signal GS propagates sequentially fromthe delay/selection circuit 52 of one sweep module 20 to thedelay/selection circuit 52 of another sweep module 20.

In each string 10, sweep control which is illustrated in FIGS. 3 and 4is executed. Here, FIG. 3 is a timing chart illustrating an example of asweep operation. Specifically, in FIG. 3, a relationship between aconnection state of the sweep modules 20 and a voltage output to thepower distribution device 5 when all the sweep modules 20 execute thesweep operation is illustrated as an example. FIG. 4 is a timing chartillustrating an example of a forcible through operation. Specifically,in FIG. 4, a relationship between a connection state of the sweepmodules 20 and a voltage output to the power distribution device 5 whensome sweep modules 20 execute the forcible through operation isillustrated as an example.

In sweep control which is executed in each string 10, the number m ofsweep modules 20 which are turned on at the same time out of a pluralityof (for example, M) sweep modules 20 incorporated into the string 10 isdetermined. The gate signal GS in sweep control has, for example, apulse-shaped waveform. In the gate signal GS, for example, a signalwaveform for connecting the battery module 30 to the main line 7 and asignal waveform for disconnecting the battery module 30 from the mainline 7 may be sequentially disposed. In the gate signal GS, the signalwaveform for connecting the battery module 30 to the main line 7 hasonly to embed the number of battery modules 30 which are connected tothe main line 7 in a predetermined period T in which the string 10 isswept. The signal waveform for disconnecting the battery module 30 fromthe main line 7 has only to embed the number of battery modules 30 whichare to be disconnected from the main line 7 out of the battery modules30 incorporated into the string 10. In the signal waveform forconnecting the battery module 30 to the main line 7 and the signalwaveform for disconnecting the battery module 30 from the main line 7,wavelengths thereof and the like are appropriately adjusted.

In each string 10 according to this embodiment, M sweep modules 20 areconnected in series in the order of sweep modules 20A, 20B, . . . , 20Mfrom the power distribution device 5. In the following description, aside which is close to the power distribution device 5 is defined as anupstream side, and a side which is distant from the power distributiondevice 5 is defined as a furthest downstream side. First, the gatesignal GS is input from the SCU 11 to the delay/selection circuit 52 ofthe sweep unit 50 in the sweep module 20A which is upstream.Subsequently, the gate signal GS propagates from the delay/selectioncircuit 52 of the sweep module 20A to the delay/selection circuit 52 ofthe sweep module 20B adjacent thereto downstream. Propagation of thegate signal to the sweep module 20 adjacent thereto downstream issequentially repeated up to the sweep module 20M which is furthestdownstream.

Here, the delay/selection circuit 52 can allow a pulse-shaped gatesignal GS which is input from the SCU 11 or the upstream sweep module 20to propagate to the downstream sweep module 20 with a delay of apredetermined delay time. In this case, a signal indicating the delaytime is input from the SCU 11 to the sweep unit 50 (the SU processingunit 51 in the sweep unit 50 in this embodiment). The delay/selectioncircuit 52 delays the gate signal GS based on the delay time indicatedby the signal. The delay/selection circuit 52 may allow the input gatesignal GS to propagate to the downstream sweep module 20 without adelay.

The gate driver 53 drives the switching operations of the firstswitching element 41 and the second switching element 42. Thedelay/selection circuit 52 outputs a signal for controlling driving ofthe gate driver 53 to the gate driver 53. The gate driver 53 outputscontrol signals to the first switching element 41 and the secondswitching element 42. When the battery module 30 is to be connected tothe main line 7, the gate driver 53 outputs a control signal for turningoff the first switching element 41 and turning on the second switchingelement 42. When the battery module 30 is disconnected from the mainline 7, the gate driver 53 outputs a control signal for turning on thefirst switching element 41 and the turning off the second switchingelement 42.

The delay/selection circuit 52 in this embodiment is controlled by acontroller such as the SCU 11 and selectively performs a sweepoperation, a forcible through operation, and a forcible connectionoperation.

For example, in the sweep operation, the first switching element 41 andthe second switching element 42 are operated by the gate signal GS. Aplurality of battery modules 30 included in the string 10 are connectedto the main line 7 in a predetermined order and is disconnected from themain line 7 in a predetermined order. As a result, the string 10 isdriven such that a predetermined number of battery modules 30 arenormally connected to the main line 7 while sequentially changing thebattery modules 30 connected to the main line 7 in a short controlcycle. Through this sweep operation, the string 10 serves as one batterypack in which the predetermined number of battery modules 30 areconnected in series while sequentially changing the battery modules 30connected to the main line 7 in the short control cycle. The sweepmodules 20 of the string 10 are controlled by the SCU 11 such that sucha sweep operation is realized. In this control, the SCU 11 outputs thegate signal GS to the string 10 and outputs the control signal to the SUprocessing unit 51 incorporated into the sweep module 20. Details of anexample of the sweep operation will be described later with reference toFIGS. 3 and 4.

In the sweep operation, the delay/selection circuit 52 outputs the inputgate signal GS to the gate driver 53 without any change and causes thegate signal GS to propagate to a downstream sweep module 20 with a delayof a delay time. As a result, the battery modules 30 of the sweepmodules 20 under the sweep operation are sequentially connected to themain line 7 and are sequentially disconnected from the main line 7 atdifferent timings in the string 10.

In the forcible through operation, the delay/selection circuit 52outputs a signal for maintaining the first switching element 41 in theON state and maintaining the second switching element 42 in the OFFstate to the gate driver 53 regardless of the input gate signal GS. As aresult, the battery modules 30 of the sweep modules 20 under theforcible through operation are disconnected from the main line 7. Thedelay/selection circuit 52 of the sweep module 20 under the forciblethrough operation causes the gate signal GS to propagate the downstreamsweep module 20 without a delay.

In the forcible connection operation, the delay/selection circuit 52outputs a signal for maintaining the first switching element 41 in theOFF state and maintaining the second switching element 42 in the ONstate to the gate driver 53 regardless of the input gate signal GS. As aresult, the battery modules 30 of the sweep modules 20 under theforcible connection operation are normally connected to the main line 7.The delay/selection circuit 52 of the sweep module 20 under the forcibleconnection operation causes the gate signal GS to propagate thedownstream sweep module 20 without a delay.

The delay/selection circuit 52 may be constituted as a single integratedcircuit that performs the above-mentioned necessary functions. Thedelay/selection circuit 52 may be constituted in combination between acircuit that delays a gate signal GS and a circuit that selectivelyoutputs a gate signal GS to the gate driver 53. An example of theconfiguration of the delay/selection circuit 52 in this embodiment willbe described below.

In this embodiment, as illustrated in FIG. 2, the delay/selectioncircuit 52 includes a delay circuit 52 a and a selection circuit 52 b.The gate signal GS input to the delay/selection circuit 52 is input tothe delay circuit 52 a. The delay circuit 52 a outputs the gate signalGS to the selection circuit 52 b with a delay of a predetermined delaytime. The gate signal GS input to the delay/selection circuit 52 isoutput to the selection circuit 52 b via another route which does notpass through the delay circuit 52 a without any change. The selectioncircuit 52 b receives an instruction signal from the SU processing unit51 and outputs the gate signal GS in accordance with the instructionsignal.

When the instruction signal from the SU processing unit 51 instructs toperform a sweep operation, the selection circuit 52 b outputs the inputgate signal GS to the gate driver 53 of the sweep module 20 without anychange. The gate driver 53 outputs a control signal to the power circuitmodule 40, turns off the first switching element 41, turns on the secondswitching element 42, and connects the battery module 30 to the mainline 7. On the other hand, the selection circuit 52 b outputs the gatesignal GS with a delay to the delay/selection circuit 52 of the sweepmodule 20 adjacent thereto downstream. That is, when the battery module30 is connected to the main line 7 in the sweep operation, the gatesignal GS with a delay of a predetermined delay time is sent to thesweep module 20 adjacent thereto downstream.

When the instruction signal from the SU processing unit 51 is theforcible through signal CSS, the selection circuit 52 b outputs a signalfor ignoring the battery module 30 to the gate driver 53. By maintainingthe forcible through signal CSS, the battery module 30 of the sweepmodule 20 receiving the forcible through signal CSS is maintained in astate in which it is disconnected from the main line 7. In this case,the selection circuit 52 b outputs the gate signal GS, which is input tothe selection circuit 52 b via another route which does not pass throughthe delay circuit 52 a, to the sweep module 20 adjacent theretodownstream.

When the instruction signal from the SU processing unit 51 is theforcible connection signal CCS, the selection circuit 52 b outputs asignal for connecting the battery module 30 to the main line 7 to thegate driver 53. That is, the gate driver 53 turns off the firstswitching element 41, turns on the second switching element 42, andconnects the battery module 30 to the main line 7. By maintaining theforcible connection signal CCS, the battery module 30 is maintained in astate in which it is connected to the main line 7. In this case, theselection circuit 52 b outputs the gate signal GS, which is input to theselection circuit 52 b via another route which does not pass through thedelay circuit 52 a, to the sweep module 20 adjacent thereto downstream.

As illustrated in FIGS. 1 and 2, in this embodiment, a plurality ofsweep units 50 (specifically a plurality of delay/selection circuits 52)included in one string 10 is sequentially connected in a daisy chainmanner. As a result, the gate signal GS input from the SCU 11 to onesweep unit 50 propagates sequentially to the plurality of sweep units50. Accordingly, processes in the SCU 11 are likely to be simplified andan increase in signal properties is easily curbed. However, the SCU 11may individually output the gate signal GS to the plurality of sweepunits 50.

Each sweep unit 50 includes an indicator 57. The indicator 57 notifiesan operator of, for example, a state of the sweep module 20 including abattery module 30 or a power circuit module 40. The indicator 57 cannotify an operator, for example, that a defect in the battery module 30of the sweep module 20 (for example, failure or deterioration of thebatteries 31) has been detected (that is, the battery module 30 shouldbe replaced).

For example, an LED which is a kind of light emitting device is used asthe indicator 57 in this embodiment. However, a device (for example, adisplay) other than an LED may be used as the indicator 57. A device(for example, a speaker) that outputs voice may be used as the indicator57. The indicator 57 may notify an operator of the state of the sweepmodule 20 by driving a member using an actuator (for example, a motor ora solenoid). The indicator 57 may be configured to indicate the stateusing different methods depending on the state of the sweep module 20.

In this embodiment, the operation of the indicator 57 is controlled bythe SU processing unit 51 of the sweep unit 50. However, a controller(for example, the SCU 11) other than the SU processing unit 51 maycontrol the operation of the indicator 57.

In this embodiment, the indicator 57 is provided for each sweep unit 50.Accordingly, an operator can easily identify the sweep module 20 ofwhich the state has been notified by the indicator 57 out of theplurality of sweep modules 20 which are arranged. However, theconfiguration of the indicator 57 may be modified. For example,separately from the indicator 57 disposed for each sweep unit 50 oralong with the indicator 57, a state notifying unit that notifies thestates of a plurality of sweep modules 20 in a bundle may be provided.In this case, for example, the state notifying unit may display thestates of the plurality of sweep modules 20 (for example, whether adefect has occurred) on one monitor.

<Sweep Control>

Sweep control which is executed in a string 10 will be described below.Here, sweep control is control for causing each battery module 30 of thestring 10 to perform a sweep operation. In sweep control which isexecuted in the string 10, the SCU 11 outputs a pulse-shaped gate signalGS. The switching elements 41 and 42 in a plurality of sweep modules 20of the string 10 are driven to switch appropriately between ON and OFF.As a result, connection of the battery module 30 to the main line 7 anddisconnection of the battery module 30 from the main line 7 are fastswitched to each other for each sweep module 20. In the string 10, thegate signal GS which is input to an X-th sweep module 20 from upstreamcan be delayed with respect to the gate signal GS which is input to an(X−1)-th sweep module 20. As a result, m (m<M) sweep modules 20connected to the main line 7 out of M sweep modules 20 in the string 10are sequentially switched. Accordingly, a plurality of battery modules30 included in the string 10 is connected to the main line 7 in apredetermined order and is disconnected from the main line in apredetermined order. A predetermined number of battery modules 30 can benormally connected to the main line 7. Through this sweep operation, thestring 10 serves as a single battery pack in which a predeterminednumber of battery modules 30 are connected in series.

FIG. 3 is a timing chart illustrating an example of a relationshipbetween connection states of sweep modules 20 and a voltage which isoutput to the power distribution device 5 when all the sweep modules 20included in the string 10 are caused to perform the sweep operation. Thenumber M of sweep modules 20 included in one string 10 can beappropriately changed. In the example illustrated in FIG. 3, five sweepmodules 20 are included in one string 10 and all of the five sweepmodules 20 are caused to perform the sweep operation.

In the example illustrated in FIG. 3, a VH command signal for setting avoltage VH [V] output to the power distribution device 5 to 100 V isinput to the SCU 11 of the string 10. The voltage Vmod [V] of thebattery module 30 in each sweep module 20 is 43.2 V. The delay time DL[μsec] by which a gate signal GS is delayed is appropriately setdepending on the specification required for the power supply system 1.The period T of the gate signal GS (that is, the period in which a sweepmodule 20 is connected and disconnected) has a value which is obtainedby multiplying the delay time DL by the number P of sweep modules 20(≤M) which are to perform the sweep operation. Accordingly, when thedelay time DL is set to be greater, the frequency of the gate signal GSbecomes lower. On the other hand, when the delay time DL is set to beless, the frequency of the gate signal GS becomes higher. In theexample, illustrated in FIG. 3, the delay time DL is set to 2.4 μsec.Accordingly, the period T of the gate signal GS is “2.4 μsec×5=12 μsec.”

In this embodiment, a battery module 30 of a sweep module 20 in whichthe first switching element 41 is turned off and the second switchingelement 42 is turned on is connected to the main line 7. That is, whenthe first switching element 41 is turned off and the second switchingelement 42 is turned on, the capacitor 47 that is provided in parallelto the battery module 30 is connected to the input and output circuit 43and electric power is input and output. The sweep unit 50 of the sweepmodule 20 connects the battery module 30 to the main line 7 while thegate signal GS is in the ON state. On the other hand, a battery module30 of a sweep module 20 in which the first switching element 41 isturned on and the second switching element 42 is turned off isdisconnected from the main line 7. The sweep unit 50 disconnects thebattery module 30 from the main line 7 while the gate signal GS is inthe OFF state.

When the first switching element 41 and the second switching element 42are simultaneously turned on, a short-circuit occurs. Accordingly, whenthe first switching element 41 and the second switching element 42 aredriven to switch, the sweep unit 50 switches one element from ON to OFFand switches the other element from OFF to ON after a slightly waitingtime has elapsed thereafter. As a result, it is possible to prevent ashort-circuit from occurring.

A VH command value which is instructed by a VH command signal is definedas VH_com, a voltage of each battery module 30 is defined as Vmod, andthe number of sweep modules 20 which are to perform the sweep operation(that is, the number of sweep modules 20 which are to be connected tothe main line 7 in sweep control) is defined as P. In this case, a dutyratio of an ON time to the period T in a gate signal GS is calculated asVH_com/(Vmod×P). In the example illustrated in FIG. 3, the duty ratio ofthe gate signal GS is about 0.46. Strictly, the duty ratio varies due toan influence of the waiting time for preventing occurrence of ashort-circuit. Accordingly, the sweep unit 50 may perform correction ofthe duty ratio using a feedback process or a feedforward process.

As illustrated in FIG. 3, when sweep control is started, first, one of Psweep modules 20 (the sweep module 20 of No. 1 which is furthestupstream in the example illustrated in FIG. 3) is connected. Thereafter,when the delay time DL elapses, a next sweep module 20 (the sweep module20 of No. 2 which is located the second from upstream in the exampleillustrated in FIG. 3) is connected. In this state, the voltage VH whichis output to the power distribution device 5 is a sum value of thevoltages of two sweep modules 20 and does not reach the VH commandvalue. When the delay time DL elapses additionally, the sweep module 20of No. 3 is connected. In this state, the number of sweep modules 20connected to the main line 7 is three of Nos. 1 to 3. Accordingly, thevoltage VH which is output to the power distribution device 5 is a sumvalue of the voltages of three sweep modules 20 and is greater than theVH command value. Thereafter, when the sweep module 20 of No. 1 isdisconnected from the main line 7, the voltage VH returns to the sumvalue of the voltages of two sweep modules 20. When the delay time DLelapses after the sweep module of No. 3 has been connected, the sweepmodule 20 of No. 4 is connected. As a result, the number of sweepmodules 20 which are connected to the main line 7 through sweep controlare three of Nos. 2 to 4. As described above, m (three in FIG. 3) sweepmodules 20 which are connected to the main line 7 out of M (five in FIG.3) sweep modules 20 are sequentially switched.

As illustrated in FIG. 3, the VH command value may not be indivisible bythe voltage Vmod of each battery module 30. In this case, the voltage VHwhich is output to the power distribution device 5 varies. However, thevoltage VH is equalized by the RLC filter and is output to the powerdistribution device 5. Even when the battery modules 30 of the sweepmodules 20 are charged with electric power which is input from the powerdistribution device 5, the connection states of the sweep modules 20 arecontrolled similarly to the timing chart illustrated in FIG. 3.

<Forcible Through Operation>

Control when some sweep modules 20 are caused to perform a forciblethrough operation and the other sweep modules 20 are caused to perform asweep operation will be described below with reference to FIG. 4. Asdescribed above, the sweep module 20 which has been instructed toperform a forcible through operation maintains a state in which thebattery module 30 is disconnected from the main line 7. The exampleillustrated in FIG. 4 is different from the example illustrated in FIG.3 in that the sweep module 20 of No. 2 is caused to perform a forciblethrough operation. That is, in the example illustrated in FIG. 4, thenumber P of sweep modules 20 which are caused to perform a sweepoperation (that is, the number of sweep modules 20 which are to beconnected to the main line 7) out of five sweep modules 20 included inone string 10 is four. The VH command value, the voltage Vmod of eachbattery module 30, and the delay time DL are the same as in the exampleillustrated in FIG. 3. In the example illustrated in FIG. 4, the periodT of the gate signal GS is “2.4 μsec×4=9.6 μsec.” The duty ratio of thegate signal GS is about 0.58.

As illustrated in FIG. 4, when some sweep modules 20 (the sweep module20 of No. 2 in FIG. 4) are caused to perform a forcible throughoperation, the number P of sweep modules 20 which are caused to performa sweep operation is less than that in the example illustrated in FIG.3. However, the string 10 adjusts the period T of the gate signal GS andthe duty ratio of the gate signal GS with the decrease in the number Pof sweep modules 20 which are caused to perform a sweep operation. As aresult, the waveform of the voltage VH which is output to the powerdistribution device 5 is the same as the waveform of the voltage VHillustrated in FIG. 3. Accordingly, the string 10 can appropriatelyoutput the commanded voltage VH to the power distribution device 5 evenwhen the number P of sweep modules 20 which are caused to perform asweep operation is increased or decreased.

For example, when a defect (for example, deterioration or failure)occurs in a battery 31 in a certain sweep module 20, the string 10 cancause the sweep module 20 including the battery 31 in which a defect hasoccurred to perform a forcible through operation. Accordingly, thestring 10 can appropriately output the commanded voltage VH to the powerdistribution device 5 using the sweep modules 20 in which a defect hasnot occurred. An operator can replace the battery module 30 includingthe battery 31 in which a defect has occurred (that is, the batterymodule 30 of the sweep module 20 which is performing a forcible throughoperation) in a state in which the string 10 is operating normally. Inother words, in the power supply system 1 according to this embodiment,it is not necessary to stop the operation of the string 10 as a wholewhen a battery module 30 is replaced.

When a certain sweep module 20 is caused to perform a forcibleconnection operation, the connection state of the sweep module 20 whichis caused to perform a forcible connection operation is a normallyconnected state. For example, when the sweep module 20 of No. 2 in FIG.4 is caused to perform a forcible connection operation instead of aforcible through operation, the connection state of No. 2 is maintainedin a “connected state” instead of a “disconnected state.”

When the power supply system 1 includes a plurality of strings 10, theabove-mentioned sweep control is executed in each of the plurality ofstrings 10. The controller (the GCU 2 in this embodiment) thatcomprehensively controls the power supply system 1 as a whole controlsthe operations of the plurality of strings 10 such that a command fromthe host system 6 is satisfied. For example, when a VH command valuerequired from the host system 6 cannot be satisfied by only one string10, the GCU 2 may satisfy the VH command value by causing the pluralityof strings 10 to output electric power.

<String>

The entire configurations of the string 10 and the power supply system 1will be described below in detail with reference to FIG. 1. As describedabove, the string 10 includes an SCU 11 and a plurality of sweep modules20 that is connected in series to the main line 7 with a power circuitmodule 40 interposed therebetween. The main line 7 of the string 10 isconnected to a bus line 9 extending from the power distribution device5. The string 10 includes a bus line voltage detecting unit 21, a systembreaker (this system breaker is appropriately referred to as a “systemmain relay (SMR)”) 22, a string capacitor 23, a string current detectingunit 24, a string reactor 25, and a string voltage detecting unit 26sequentially from the power distribution device 5 side (upstream) in themain line 7. Disposition of some members may be modified. For example,the system breaker 22 may be provided downstream from the stringcapacitor 23.

The bus line voltage detecting unit 21 detects a voltage of the bus line9 extending from the power distribution device 5 to the string 10. Thesystem breaker 22 switches between connection and disconnection betweenthe string 10 and the power distribution device 5. In this embodiment,the system breaker 22 is driven in accordance with a signal which isinput from the SCU 11. The string capacitor 23 and the string reactor 25form an RLC filter to achieve equalization of a current. The stringcurrent detecting unit 24 detects a current flowing between the string10 and the power distribution device 5. The string voltage detectingunit 26 detects a total voltage of voltages of the plurality of sweepmodules 20 which is connected in series to the main line 7 in the string10, that is, a string voltage of the string 10.

In the example illustrated in FIG. 1, the system breaker 22 includes aswitch 22 a and a fuse 22 b. The switch 22 a is a device that connectsor disconnects the string 10 to and from the power distribution device5. The switch 22 a can be appropriately referred to as a string switch.By turning on the switch 22 a, the main line 7 of the string 10 isconnected to the bus line 9 of the power distribution device 5. Byturning off the switch 22 a, the string 10 is disconnected from thepower distribution device 5. The switch 22 a is controlled by the SCU 11controlling the string 10. By operating the switch 22 a, the string 10can be appropriately disconnected from or connected to the powerdistribution device 5. The fuse 22 b is a device that stops anunexpected large current when the large current flows in the main line 7of the string 10 in view of design of the string 10. The fuse 22 b isalso appropriately referred to as a string fuse.

Here, when batteries incorporated into one battery module 30 have thesame standard, the voltage of one battery module 30 increases as thenumber of batteries incorporated increases. On the other hand, when thevoltage of one battery module 30 is high, the battery module isdangerous for an operator to handle and is heavy. In this regard, asmany batteries as possible may be incorporated into one battery module30 within a range of a voltage with which an operator will not besubjected to a significant accident even with touch of the operator withthe fully charged battery module (for example, lower than 60 V andpreferably lower than 42 V) and within a range of a weight with which anoperator can easily replace the battery module. The battery module 30which is incorporated into the string 10 does not need to include thesame batteries, and the number of batteries which are incorporated intoone battery module 30 can be determined depending on types, standards,or the like of the batteries which are incorporated into the batterymodule 30. The string 10 is configured to output a necessary voltage bycombining sweep modules 20 into which the battery module 30 has beenincorporated in series. The power supply system 1 is configured tooutput electric power required for connection to the power system 8 bycombining a plurality of strings 10.

In this embodiment, the power distribution device 5 to which a pluralityof strings 10 of the power supply system 1 is connected includes subpower distribution devices 5A and 5B that are connected to the strings10A and 10B. The strings 10A and 10B connected to the sub powerdistribution devices 5A and 5B are connected in parallel via the subpower distribution devices 5A and 5B. The power distribution device 5controls distribution of electric power which is input to the strings10A and 10B from the power system 8, combination of electric power whichis output from the strings 10A and 10B to the power system 8, and thelike through the sub power distribution devices 5A and 5B connected tothe strings 10. The power distribution device 5 and the sub powerdistribution devices 5A and 5B are controlled such that the power supplysystem 1 into which a plurality of strings 10 is incorporated serves asa single power supply device as a whole by cooperation between the GCU 2connected to the host system 6 and the SCU 11 that controls each string10.

For example, in this embodiment, a downstream side from the powerdistribution device 5, that is, the strings 10A and 10B side, iscontrolled with a direct current. An upstream side from the powerdistribution device 5, that is, the power system 8, is controlled withan alternating current. The voltages of the strings 10A and 10B arecontrolled to be roughly balanced with the voltage of the power system 8via the power distribution device 5. When the voltage of each of thestrings 10A and 10B is controlled to be lower than that of the powersystem 8, a current flows from the power system 8 to each of the strings10A and 10B. At this time, when sweep control is executed in the strings10A and 10B, the battery modules 30 are appropriately charged. When thevoltage of each of the strings 10A and 10B is controlled to be higherthan that of the power system 8, a current flows from each of thestrings 10A and 10B to the power system 8. At this time, when sweepcontrol is executed in the strings 10A and 10B, the battery modules 30are appropriately discharged. The power distribution device 5 maymaintain the voltages of the strings 10A and 10B to be equal to thevoltage of the power system 8 such that a current hardly flows in thestrings 10A and 10B. In this embodiment, this control can be executedfor each of the sub power distribution devices 5A and 5B to which thestrings 10A and 10B are connected. For example, by adjusting the voltagefor each of the strings 10A and 10B, control may be executed such that acurrent hardly flows in some string 10 out of a plurality of strings 10Aand 10B connected to the power distribution device 5.

In the power supply system 1, the total capacity of the power supplysystem 1 can be increased by increasing the number of strings 10 whichare connected in parallel to the power distribution device 5. Forexample, with the power supply system 1, it is possible to construct alarge system that can output electric power such that a sudden increasein demand in the power system 8 can be absorbed or can supplement suddenpower shortage in the power system 8. For example, by increasing thecapacity of the power supply system 1, great surplus electric power ofthe power system 8 can be appropriately transferred to charging of thepower supply system 1. For example, when output power of a power plantis surplus in a night time zone in which demand for electric power islow or when an amount of electric power generated in a largephotovoltaic system increases suddenly, the power supply system 1 canabsorb surplus electric power via the power distribution device 5. Onthe other hand, when demand for electric power in the power system 8increases suddenly, necessary electric power can be appropriately outputfrom the power supply system 1 to the power system 8 via the powerdistribution device 5 in accordance with a command from the host system6. Accordingly, with the power supply system 1, power shortage in thepower system 8 is appropriately supplemented.

In the power supply system 1, it is not necessary to normally connectall battery modules 30 out of a plurality of battery modules 30 which isincorporated into a string 10. Since a forcible through operation can beperformed for each battery module 30 as described above, a batterymodule 30 in which a defect has occurred can be disconnected from sweepcontrol of the string 10 when a defect has occurred in the batterymodule 30. Accordingly, in the power supply system 1, a battery which isused for the battery module 30 does not need to be a new battery whichhas not been used.

For example, a secondary battery which has been used as a driving powersource of a motor-driven vehicle such as a hybrid vehicle or an electricvehicle can be appropriately reused. Even when such a secondary batterywhich has been used as a driving power source is used, for example, forabout 10 years, the secondary battery can satisfactorily perform asecondary battery function. In the power supply system 1, since abattery module 30 in which a defect has occurred can be immediatelydisconnected, a battery can be incorporated into the battery module 30,for example, by ascertaining that the battery performs a necessaryfunction. The time for sequentially recovering a secondary battery whichhas been used as a driving power source of a motor-driven vehicle comesup. With the power supply system 1, for example, secondary batteriescorresponding to 10,000 motor-driven vehicles may be incorporatedthereinto and thus considerable recovered secondary batteries can beabsorbed. It cannot be seen when a secondary battery which has been usedas a driving power source of a motor-driven vehicle deteriorates inperformance. When such a secondary battery is reused for a batterymodule 30 of the power supply system 1, it is not possible to predictwhen a defect occurs in the battery module 30.

With the power supply system 1 which has been proposed herein, it ispossible to appropriately disconnect a battery module 30 via a sweepmodule 20. Accordingly, even when a defect occurs suddenly in a batterymodule 30 or a secondary battery incorporated into the battery module30, it is not necessary to stop the power supply system 1 as a whole.

<Detection of Failure of Switching Element>

As described above, in the power supply system 1 according to thisembodiment, MOSFETs are used as the switching elements 41 and 42. Sincethe switching elements 41 and 42 formed of MOSFETs include body diodes41 a and 42 a, a current may flow via the body diodes 41 a and 42 a evenwhen the switching elements 41 and 42 have a disconnection failure.Accordingly, even when the switching elements 41 and 42 in one sweepmodule 20 out of a plurality of sweep modules 20 incorporated in astring 10 have a disconnection failure, electric power with a normalvoltage and a normal current can be input to and output from the string10 as a whole and thus it is difficult to promptly detect a position atwhich the switching elements 41 and 42 have a disconnection failure.

The power supply system 1 includes a failure detecting device thatdetects a disconnection failure of the switching elements 41 and 42. Thefailure detecting device includes a temperature detecting unit 48 and afailure determining unit. The temperature detecting unit 48 isconfigured to detect temperatures of a plurality of sweep modules 20.The failure determining unit is configured to determine whether adifference (T_(m)−T_(s)) between a temperature T_(m) of one sweep module20 (a sweep module 20 which is an inspection object) which is selectedfrom the plurality of sweep modules 20 and a reference temperature T_(s)which is determined based on the temperatures of the other sweep modules20 is greater than a predetermined threshold value ΔT_(th). With thepower supply system 1 including the failure detecting device, it ispossible to easily detect whether the switching elements 41 and 42 of asweep module 20 which is an inspection object have a failure. Thefailure determining unit may be configured as a sub function of acontrol device such as the sweep unit 50 or the SCU 11.

A failure determining process for the switching elements 41 and 42 inthe power supply system 1 according to this embodiment will bespecifically described below. First, the SCU 11 transmits a connectionsignal to a plurality of sweep modules 20 including a sweep module 20which is an inspection object. The sweep module 20 to which theconnection signal has been input turns off the first switching element41 of the power circuit module 40, turns on the second switching element42, and connects the battery module 30 to the main line 7. Asillustrated in FIG. 5, when a charging current flows in the main line 7in a state in which the switching elements 41 and 42 are switched inthis way, a current flows in the direction of arrow A in the drawing. Atthis time, when the second switching element 42 is normal, the currentflows through the second switching element 42 and thus a degree ofincrease in temperature of the sweep module 20 is small. On the otherhand, when a charging current flows in the direction of arrow A in astate in which the second switching element 42 has a disconnectionfailure, a current flows into the second body diode 42 a and the secondbody diode 42 a emits heat. In this way, in the sweep module 20 in whichthe second switching element 42 has a disconnection failure, when acharging current flows in the main line 7 at the time of transmission ofthe connection signal, the second body diode 42 a emits heat and thesubstrate temperature increases greatly.

In this embodiment, whether an increase in substrate temperature due toemission of heat from the second body diode 42 a is caused is determinedbased on the result of detection from the temperature detecting unit 48.As illustrated in FIG. 2, the temperature detecting unit 48 includes atemperature sensor which is disposed at an intermediate position betweenthe first switching element 41 and the second switching element 42,detects temperature information at the intermediate position, andtransmits the detected temperature information to the SU processing unit51. The SU processing unit 51 processes the received temperatureinformation as a “temperature of the sweep module 20” and transmits theprocess result to the SCU 11 (see FIG. 1). In this embodiment, thetemperatures of the plurality of sweep modules 20 which are disposed inthe string 10 are transmitted to the SCU 11.

Then, the SCU 11 selects the temperature T_(m) of one sweep module outof the received temperatures of the plurality of sweep modules 20 andsets the selected temperature as a “temperature T_(m) of a sweep modulewhich is an inspection object.” The SCU 11 calculates an average valueT_(ave-m) of the temperatures of the sweep modules other than theselected sweep module which is an inspection object and sets the“average value T_(ave-m) of the temperatures of the other sweep modules”as a “reference temperature T_(s).” Then, the SCU 11 calculates adifference (T_(m)−T_(ave-m)) between the “temperature T_(m) of the sweepmodule which is an inspection object” and the “average value T_(ave-m)of the temperatures of the other sweep modules.” Then, the SCU 11determines whether the difference (T_(m)−T_(ave-m)) is greater than apredetermined threshold value ΔT_(th). When it is determined in thefailure determining process that the difference (T_(m)−T_(ave-m)) isgreater than the threshold value ΔT_(th), it is determined that anexcessive increase in temperature has been caused due to emission ofheat from the second body diode 42 a in the sweep module which is aninspection object, that is, that the second switching element 42 has adisconnection failure. In this way, according to this embodiment, evenwhen the second switching element 42 formed of a MOSFET is used, it ispossible to easily detect whether the second switching element 42 of thesweep module 20 which is an inspection object has a failure.

The SCU 11 according to this embodiment sequentially determines whetherthe difference (T_(m)−T_(ave-m)) is greater than the threshold valueΔT_(th) while changing the sweep module which is an inspection objectout of the plurality of sweep modules 20 in the string 10. That is, theSCU 11 according to this embodiment sequentially performs the failuredetermining process on all the sweep modules while changing the sweepmodule which is an inspection object. Accordingly, in the power supplysystem 1 including a plurality of sweep modules 20, it is possible toeasily identify a sweep module in which the second switching element 42has a failure.

The threshold value ΔT_(th) in the failure determining process can beset in advance in consideration of a performance or a usage environmentof the second switching element 42 or the like. An example of a processof setting the threshold value ΔT_(th) will be described below. Here, adrain-source resistance when the second switching element 42 is turnedon is defined as “R_(DS(ON))” and a forward voltage of the second bodydiode 42 a is defined as “V_(SD).” The ambient temperature of a sweepmodule 20 is defined as “T_(a),” the temperature of the sweep module 20which is detected by the temperature detecting unit 48 is defined as“T_(b),” and the current of the battery module 30 is defined as “I(A).”In this case, an increase in temperature (ΔT) in a sweep module 20 inwhich the second switching element 42 is normal is represented byExpression (1), and an increase in temperature (ΔT′) in a sweep module20 in which the second switching element 42 has a disconnection failureis represented by Expression (2).ΔT=T _(b) −T _(a) ∝R _(DS(ON)) ·I ²  (1)ΔT′=T _(b) −T _(a) ∝V _(SD) ·I  (2)

A rate of change in temperature (ΔT′/ΔT) of ΔT′ to ΔT is represented byExpression (3).ΔT′/ΔT∝V _(SD) ·I/R _(DS(ON)) ·I ²  (3)

The threshold value ΔT_(th) in the failure determining process can beset, for example, based on Expression (3). For example, when a MOSFET(type: IPB065N15N3) made by Infineon Technologies AG is used as thesecond switching element 42, R_(DS(ON)) is 5 mΩ and V_(SD) is 1.0 V.When it is assumed that the current I of the battery module 30 is 50 A,ΔT′/ΔT∝4 is obtained. The threshold value ΔT_(th) is temporarily setbased thereon as represented by Expression (4). The SCU 11 sets aspecific threshold value ΔT_(th) by substituting the temperatureinformation for the difference “T_(m)−T_(ave-m)” into Expression (4) atthe time of performing the failure determining process.ΔT _(th)=(T _(ave-m) −T _(a))×0.5  (4)

A failure determining process for the first switching element 41 will bedescribed below. When a failure of the first switching element 41 isdetected, the SCU 11 transmits a disconnection signal to a plurality ofsweep modules 20 including a sweep module 20 which is an inspectionobject. A sweep module 20 to which the disconnection signal has beeninput turns on the first switching element 41 of the power circuitmodule 40, turns off the second switching element 42, and disconnectsthe battery module 30 from the main line 7. As illustrated in FIG. 6,when a discharging current flows in the main line 7 in this state, acurrent flows in the direction of arrow B. At this time, when the firstswitching element 41 is normal, a current passing through the firstswitching element 41 flows and thus a degree of increase in temperatureof the sweep module 20 is small. On the other hand, when the firstswitching element 41 has a disconnection failure and a dischargingcurrent flows in the direction of arrow B, a current flows into thefirst body diode 41 a and the first body diode 41 a emits heat. In thisway, in a sweep module 20 in which the first switching element 41 has adisconnection failure, when a discharging current flows in the main line7 at the time of transmission of the disconnection signal, the firstbody diode 41 a emits heat to greatly increase the substratetemperature.

Similarly to the above-mentioned determination of whether the secondswitching element 42 has a failure, the SCU 11 receives a “temperatureof a sweep module 20” from the SU processing unit 51 of each sweepmodule 20 to which the disconnection signal has been transmitted. TheSCU 11 selects a “temperature T_(m) of a sweep module which is aninspection object” out of the received temperatures of the plurality ofsweep modules 20, calculates an “average value T_(ave-m) of thetemperatures of the other sweep modules”, and sets the calculatedaverage value as the “reference temperature T_(s).” Then, the SCU 11calculates a difference (T_(m)−T_(ave-m)) therebetween and determineswhether the difference (T_(m)−T_(ave-m)) is greater than the thresholdvalue ΔT_(th). When the difference (T_(m)−T_(ave-m)) is greater than thethreshold value ΔT_(th), the SCU 11 determines that the first switchingelement 41 in the sweep module 20 which is an inspection object has adisconnection failure. In this way, according to this embodiment, it ispossible to easily detect whether the first switching element 41 in asweep module 20 which is an inspection object has a failure.

Then, similarly to the failure determining process for the secondswitching element 42, the SCU 11 sequentially performs the failuredetermining process on all the sweep modules 20 while changing the sweepmodule which is an inspection object in the failure determining processfor the first switching element 41. Accordingly, in a power supplysystem 1 including a plurality of sweep modules 20, a sweep module inwhich the first switching element 41 has a failure can be easilyidentified.

The threshold value ΔT_(th) in the failure determining process for thefirst switching element 41 can be set in the same processes as for thethreshold value ΔT_(th) in the failure determining process for thesecond switching element 42 and thus detailed description thereof willnot be repeated.

When a sweep module 20 in which at least one of the first switchingelement 41 and the second switching element 42 has a failure isidentified through the failure determining process, the SCU 11 transmitsa failure signal to the SU processing unit 51 of the sweep module 20.The SU processing unit 51 causes the failure signal to be transmitted tothe indicator 57 and notifies an operator that the switching elements 41and 42 have a disconnection failure via the indicator 57. In this way,with the power supply system 1 according to this embodiment, a sweepmodule in which the temperature has increased due to a disconnectionfailure of the switching elements 41 and 42 can be identified bycomparison with other sweep modules, thereby contributing to improvementin safety of the power supply system 1.

While the power supply system 1 according to an embodiment of thedisclosure has been described above, the disclosure is not limited tothe embodiment.

For example, in the above-mentioned embodiment, one temperature sensoris provided at an intermediate position between the first switchingelement 41 and the second switching element 42 and a temperaturedetected at the intermediate position is defined as a “temperature of asweep module” in view of a decrease in the number of components.However, the number of temperature sensors or the positions thereof arenot limited to those of the embodiment. For example, the temperaturedetecting unit may individually include a first temperature sensor thatis disposed in the vicinity of the first switching element and a secondtemperature sensor that is disposed in the vicinity of the secondswitching element. When two temperature sensors are provided in thisway, temperature information from the first temperature sensor when thefailure determining process for the first switching element is performedcan be considered as the “temperature of a sweep module” and temperatureinformation from the second temperature sensor when the failuredetermining process for the second switching element is performed can beconsidered as the “temperature of a sweep module.” In this way, it ispossible to more accurately detect a failure of a switching element byswitching a temperature sensor which is to be used depending on adetermination object.

The failure determining unit in the power supply system 1 can beconfigured to determine whether the difference (T_(m)−T_(s)) between thetemperature T_(m) of a sweep module which is an inspection object andthe reference temperature T_(s) is greater than the threshold valueΔT_(th), and the sequence of the failure determining process is notlimited to the above-mentioned embodiment.

For example, whether the difference (T_(m)−T_(s)) is greater than thethreshold value ΔT_(th) may be determined a plurality of times and itmay be determined that the switching element of the sweep module whichis an inspection object has a disconnection failure when the number oftimes in which the difference (T_(m)−T_(s)) is greater than thethreshold value ΔT_(th) is greater than a predetermined reference value.Accordingly, it is possible to prevent erroneous operation due to noisesuch as that in an ambient temperature and to more accurately detect adisconnection failure of the switching element.

In the above-mentioned embodiment, the “average value T_(ave-m) of thetemperatures of the sweep modules other than the sweep module which isan inspection object” is employed as the reference temperature T_(s),but another value may be employed as the reference temperature T_(s).For example, when the “average value T_(ave-m) of the temperatures ofthe other sweep modules” is calculated, a sweep module to which aforcible through signal or a forcible connection has been transmittedmay be excluded. Accordingly, it is possible to more accurately performthe failure determining process. A plurality of sweep modules forsetting a reference temperature may be arbitrarily selected and the“average value of the temperatures of the sweep modules for setting areference temperature” may be used as the reference temperature T_(s).The reference temperature T_(s) is not limited to the average value ofthe temperatures of a plurality of sweep modules and a value other thanthe average value may be employed. For example, the temperature of asweep module in which the switching elements are ascertained to benormal may be employed as the reference temperature T_(s). The referencetemperature T_(s) and the temperature T_(m) of a sweep module which isto be inspected may be an increase in temperature per unit time (a rateof increase in temperature). From the viewpoint of a decrease ininfluence of surrounding environments or operating states of the powersupply system, the average value of the temperatures of a plurality ofsweep modules can be used as the reference temperature T_(s).

In the above-mentioned embodiment, the failure determining process issequentially performed on all the sweep modules 20 while changing thesweep module which is an inspection object. However, all the sweepmodules 20 do not need to be set as an inspection object, and a sweepmodule which is an inspection object may be appropriately selected ifnecessary. For example, by setting a sweep module in which the switchingelement is suspected to have a failure as an inspection object andperforming the failure determining process thereon, it is possible toascertain whether the switching element of the sweep module has afailure. A sweep module to which a forcible through signal or a forcibleconnection signal has been transmitted may be excluded from theinspection objects and the other sweep modules may be sequentially usedas the inspection object.

While a specific embodiment of the disclosure has been described abovein detail, the embodiment is only an example and does not limit theappended claims. The technique described in the claims includes variousmodifications and changes to the above-mentioned embodiment.

What is claimed is:
 1. A power supply system comprising: a main line; aplurality of sweep modules that is connected to the main line; and afailure detecting device, wherein each sweep module includes a batterymodule, an input and output circuit that is configured to connect thebattery module to the main line, at least one switching element that isprovided in the input and output circuit, is configured to switchbetween connection and disconnection between the battery module and themain line, and is formed of a MOSFET, and a switching control unitconfigured to transmit a gate signal to the at least one switchingelement, and wherein the failure detecting device includes a temperaturedetecting unit configured to detect temperatures of the plurality ofsweep modules, and a failure determining unit configured to determinewhether a difference (T_(m)−T_(s)) between a temperature T_(m) of onesweep module selected from the plurality of sweep modules and areference temperature T_(s) which is determined based on thetemperatures of other sweep modules is greater than a predeterminedthreshold value ΔT_(th).
 2. The power supply system according to claim1, wherein the failure determining unit is configured to sequentiallydetermine whether the difference (T_(m)−T_(s)) is greater than thepredetermined threshold value ΔT_(th) while changing the sweep modulewhich is selected from the plurality of sweep modules.
 3. The powersupply system according to claim 1, wherein the reference temperatureT_(s) is an average value T_(ave-m) of the temperatures of the othersweep modules other than the sweep module which is selected from theplurality of sweep modules.
 4. The power supply system according toclaim 1, wherein each sweep module includes: a first switching elementthat is attached in series to the main line and in parallel to thebattery module; and a second switching element that is attached to theinput and output circuit such that the battery module is connected inseries to the main line, wherein the switching control unit isconfigured to transmit a connection signal for connecting the batterymodule to the main line by turning off the first switching element andturning on the second switching element, and a disconnection signal fordisconnecting the battery module from the main line by turning on thefirst switching element and turning off the second switching element,and wherein the temperature detecting unit includes: a temperaturesensor that is disposed at an intermediate position between the firstswitching element and the second switching element; and a processingunit configured to detect the temperature of the sweep module based on asignal transmitted from the temperature sensor.
 5. The power supplysystem according to claim 4, wherein the failure determining unit isconfigured to select a sweep module to which the connection signal hasbeen transmitted from the switching control unit when a charging currentis flowing in the main line and to determine that the second switchingelement of the selected sweep module has a failure when the difference(T_(m)−T_(s)) between the temperature T_(m) of the selected sweep moduleand the reference temperature T_(s) is greater than the predeterminedthreshold value ΔT_(th).
 6. The power supply system according to claim4, wherein the failure determining unit is configured to select a sweepmodule to which the disconnection signal has been transmitted from theswitching control unit when a discharging current is flowing in the mainline and to determine that the first switching element of the selectedsweep module has a failure when the difference (T_(m)−T_(s)) between thetemperature T_(m) of the selected sweep module and the referencetemperature T_(s) is greater than the predetermined threshold valueΔT_(th).